According to the estimates of the World Health Organization (WHO), the number of people with diabetes will increase from 177 million in 2000 to 300 million by 2025. It is also estimated that 9% of all deaths worldwide are due to diabetes. Although diabetes is presently not curable, intensive insulin therapy in diabetic patients can dramatically delay the onset of serious complications.
The cornerstone to tight glycemic control is frequent or even continuous glucose monitoring, where blood glucose concentrations are measured to help administer proper levels of insulin and maintain euglycemic conditions. Continuous glucose monitoring (in practice a measurement every few minutes) is the prerequisite to enable strict glycemic control lowering the blood glucose levels within a “healthy” range (80-110 mg/dL) that prevents medical complications while avoiding dangerously low blood glucose concentrations (hypoglycemia). The ability to maintain blood glucose levels within this healthy range requires frequent measurements of glucose concentrations in the blood. Each measurement provides information that can be used to deliver the proper amount and type of insulin to maintain blood glucose levels within the targeted concentration range.
It is demonstrated that tight or continuous blood glucose control can introduce substantial reductions in overall medical care costs. Glucose sensing technology has advanced considerably in recent years, thereby providing excellent tools for home glucose monitoring and establishing opportunities for tight glycemic control. Unfortunately, the cost and pain associated with current glucose test-strip technology generally restrict the number of daily measurements performed by the average person with diabetes (on average 4-6 times a day).
Examples of next-generation sensors are implantable glucose bio-sensors. To date, implantable glucose sensors are all based on surface chemical reactions. Such sensors are very stable, accurate and sensitive in vitro. However, once the sensors are implanted, the stability and reliability reduces dramatically after a few days owing in large part to fouling of the sensor surface by proteinaceous material. They can therefore not be used for long term implantation. Alternative sensors under study are based on spectrometric devices which should allow long term in vivo operation thus justifying the surgical procedure to implant the device.
Some initiatives in the domain of subcutaneously implantable spectroscopic sensors are already reported. In US2007/0066877 A1, an implantable sensor device is established. In vitro testing confirms practicability of the invasive concept and the feasibility of target specifications. The device has a fluid inlet port, a measurement volume and a fluid outlet port. Bodily fluid and/or target analyte is forced to the measurement volume using micro-dialisis or ultra-filtration with vacuum source and analysed using a spectrometer. In “Optical Absorption Glucose Measurements Using 2.3-μm Vertical-Cavity Semiconductor Lasers” IEEE phot. Tech. lett., 20(11), pp. 930-933, 2008, the development of a 2.3 μm vertical-cavity semiconductor laser (VCSEL) is reported for applications wherein the tunable VCSEL and detector are packaged as an implantable design. However the finite tuning range of 5 nm that can be reached with the VCSEL limits the potential for in vivo use of the radiation source.